The game uses 'puzzle-piece' board sections that can be recombined to construct different mission scenarios.

One ('evil') player has more information than the other, because their pieces are represented as 'blips on the radar' for part of the game. (This means that the 'good' player must guess at the relative strength of the enemy forces in different board areas.)

The board sections have a semantics (meaning) in the game: flame weapons, among others, affect whole sections at once.

The 'good' player can make moves in the 'evil' player's turn under certain conditions.

The 'good' player has restricted thinking time each turn -- around three minutes.

The setting is a huge spaceship (hulk) which is infested with Stealers and, as such, poses a threat to humanity. The 'evil' player controls endless hordes of Genestealers, vicious aliens, who steadily reinforce throughout the game.
The 'good' player controls a squad or two of Space Marines&trade, human soldiers, in Terminator armour (a thick exoskeleton). You may be able to spot parallels with the film 'Aliens'.

The Space Marines must skilfully employ their firepower to prevent the numerous Stealers from getting too close. The Genestealers are ferocious in close-quarters combat but can't use ranged weapons at all. Because of the unequal standing of the two sides in many missions, Space Hulk is well suited to match play (where the players switch sides, playing each scenario through twice or more).

There is a free computer implementation of Space Hulk, called 'Sulk'. There is also one called 'QSpacehulk', but it's not as nice, nor is it by me.

Official computer versions of Space Hulk were produced, first for Atari and then PC. They are not implementations of the original board game, but arcade-style interpretations.

This is largely excised from my Sulk manual at http://sulk.sf.net/manual . All trademarks are held by Games Workshop.